Particle exclusion and accumulation prevention using nanoforest filters on downhole tools

ABSTRACT

A reaming tool includes a tubular body having an axial cavity and a plurality of housings. Each of the housings has an opening through a periphery of the tubular body. A cutter element is positioned in each of the housings, and the cutter element is movable between a retracted position and an extended position. A drive mechanism is positioned within the tubular body and is movable relative to the tubular body to extend or retract each cutter element. A gap is defined between the drive mechanism and the tubular body. A carbon nanotube forest is coupled to one of the drive mechanism and the tubular body to reduce or prevent accumulation of particles in the gap.

FIELD

The present disclosure relates generally to downhole tools associated with the recovery of subterranean deposits and more specifically to a system and method for preventing the accumulation of particles in a downhole tool.

DESCRIPTION OF RELATED ART

Wells are drilled to various depths to access and produce oil, gas, minerals, and other naturally-occurring deposits from subterranean geological formations. The drilling of a well typically is accomplished with a drill bit that is rotated to advance the wellbore by removing topsoil, sand, clay, limestone, calcites, dolomites, or other materials. As the drill bit advances, significant amounts of debris result from the drilling process. As fluid is pumped downhole to remove debris from the well, particles may accumulate around and within downhole tools and the operation of these tools may be affected. Particle accumulation in and around joints, gaps, passages, and other areas of tools may result in premature wear of the tools or prevent the proper operation of the tools.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional side view of a reaming tool according to an illustrative embodiment, the reaming tool having cutting arms shown in a retracted position;

FIG. 2 illustrates a side view of the reaming tool of FIG. 1, the cutting arms shown in an extended position;

FIG. 3 illustrates an enlarged side view of a portion of the reaming tool of FIG. 2;

FIG. 4 illustrates an elevation view of a drilling rig having carbon nanoforests according to an illustrative embodiment;

FIGS. 5A and 5B illustrate cross-sectional side and end views, respectively, of a downhole tool having a carbon nanoforest according to an illustrative embodiment;

FIG. 6A illustrates a side view of a reaming tool having a carbon nanoforest according to an illustrative embodiment, the reaming tool having cutter blocks shown in a retracted position;

FIG. 6B illustrates a side view of the reaming tool of FIG. 6A, the cutter blocks shown in an extended position;

FIG. 7 illustrates a sequential schematic view of a carbon nanoforest being grown on a mating surface of a joint according to an illustrative embodiment; and

FIG. 8 illustrates a sequential schematic view of a carbon nanoforest being grown on a substrate and subsequently adhesively coupled to a mating surface of a joint.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of the illustrative embodiments, reference is made to the accompanying drawings that form a part hereof. These embodiments are described in sufficient detail to enable those skilled in the art to practice what is disclosed; and it is understood that other embodiments may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the disclosure. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense; and the scope of the illustrative embodiments is defined only by the appended claims.

Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion and, thus, should be interpreted to mean “including, but not limited to.” Unless otherwise indicated, as used throughout this document, “or” does not require mutual exclusivity.

The embodiments described herein relate to systems, tools, and methods that use carbon nanoforests as filters for particle exclusion and coatings to prevent the adhesion of material. As used herein, the term “carbon nanoforest” may refer to a plurality of carbon nanostructures that may be vertically aligned. In other words, a long axis of the nanostructure may extend substantially perpendicular from a substrate to which the nanostructure is coupled. A carbon nanoforest may include single-walled carbon nanotubes (“SWNTs”), multi-walled carbon nanotubes (“MWNTs”) (e.g., 2 to 50 or more walls), carbon nanohorns, graphene, graphene nanoribbons, other elongated carbon nanostructures, or a combination of these structures. It should be noted that reference to graphene encompasses few-layer graphene.

As described herein, carbon nanoforests act as an effective and durable filter in areas where particulates may otherwise infiltrate mechanical systems or downhole tools. Also, the presence of a carbon nanoforest on a surface may enhance the resistance of the surface to particle accumulation by effectively providing a smaller surface area to which particles may attach. When a particle encounters and contacts a carbon nanoforest, the particle may only touch the narrow ends of the carbon nanostructures and not a solid, uninterrupted surface as would be the case if the carbon nanoforests were not present. Similarly, particle contact with the elongated walls of individual nanostructures creates less adhesion than if the particle was contacting a solid surface. When surface contact is minimized in this way, the adhesion forces and static friction between the particles and the carbon nanoforest may be significantly lower than a surface that does not include a carbon nanoforest.

When deployed in downhole drilling operations as disclosed herein, carbon nanoforests may act as a filter to reduce or prevent particles from reaching and accumulating in critical areas that may otherwise experience high particle accumulation. The benefits of low particle adhesion to carbon nanoforests include the ability of the carbon nanoforest to be flushed of particles as fluid circulates near the carbon nanoforest. In various embodiments described herein, a carbon nanoforest filter may be deployed at entrances to joints, along passages to joints, or in other areas where particle or debris accumulation is likely. Likely accumulation areas may be determined by engineering analysis or by observation. Joints or gaps at which two or more parts of a tool meet must move and have clearance to move, and these joints are but one example of an area for which protection may be desired. Furthermore, the carbon nanoforests may be deployed in areas where fluid movement may be reduced and fluids tend to stagnate.

FIGS. 1 and 2 are cross-sectional side views of a reaming tool 80 having a carbon nanoforest strategically applied at different locations to minimize or prevent the accumulation of undesirable particles at potential accumulation zones. The reaming tool 80 includes a tubular body 1 to be mounted within a drill string. The tubular body 1 includes an axial cavity 2 in which drilling muds may circulate. The tubular body 1 further includes one or more housings 3 provided with openings through a periphery of tubular body 1. An exterior region of the reaming tool 80 is the region around the tubular body 1 that is exposed to wellbore fluids during deployment of the reaming tool 80 in a wellbore.

In the example illustrated, a cutter element 4 is housed in each housing 3 and includes two cutting arms 5 and 6 operable to articulate relative to one another. Cutting arm 5 is articulated on tubular body 1 by pivot shaft 7 and on cutting arm 6 by pivot shaft 8. Cutting arm 6 is also articulated by pivot shaft 9 on a transmission mechanism, which is, in the example illustrated, in the form of a transmission element 10. A retracted position of cutting arms 5 and 6 in each housing 3 is illustrated in FIG. 1, and an extended position is illustrated in FIG. 2.

Cutter elements 4 may have more than two articulated cutting arms. Moreover, cutter elements 4 are provided with cutting tips, and the surfaces of cutting arms 5 and 6 in the extended position include a front area 11. Front area 11 is inclined towards the front, or downhole, side of the tool, and is intended to produce an enlargement of the borehole during the descent of the tool. Cutting arms 5 and 6 also include a central area 12 that may be substantially parallel to an axis of the tool when the cutting arms 5 and 6 are in the extended position. Central area 12 is intended to stabilize the tool with respect to the broadened hole. It is also possible to provide a rear, or uphole, area of the cutting arms 5 and 6 with cutting tips operable to produce a broadening of the borehole when the drill string is being raised.

Housings 3 are recessed into tubular body 1 and extend inward almost to axial cavity 2. Each housing 3 has a bottom wall 20 (FIG. 2), two parallel lateral walls 21 and 22 (FIG. 1), and two front walls 23 and 24 (FIG. 1). The full depth of housing 3 may be occupied by cutting arms 5 and 6. In this way, the thickness of the cutting arms 5 and 6 may be maximized because the majority of the diameter of tubular body 1 not dedicated to axial cavity 2 may be occupied by cutting arms 5 and 6.

In the extended position, cutting arms 5 and 6 form a space 14 between the cutting arms 5 and 6 and the tubular body 1. The space 14 has a triangular shape in a profile view, and is closed off from the drilling muds circulating outside tubular body 1. As can be seen in FIG. 2, the angle at a vertex 13 of this triangular space 14 is also situated inside the housing 3 defined by tubular body 1, and cuttings resulting from underreaming, or from a drilling operation, typically cannot enter this closed, triangular space 14.

A drive mechanism, which in the example embodiment illustrated is provided in the form of a hollow piston 15, is arranged inside the tubular body 1. Hollow piston 15 is in a position axially offset with respect to cutter elements 4. A transmission element 10 is disposed in each housing 3 and is capable of moving longitudinally therein. At an end opposite to that articulated on cutting arm 6, each transmission element 10 includes a projection 16 which enters inside tubular body 1 through an elongate slot 17. Transmission elements 10 bear on hollow piston 15 and follow hollow piston 15 as hollow piston 15 axially moves.

Hollow piston 15 separates axial cavity 2 from tubular body 1, and also separates axial cavity 2 from housings 3. In the example illustrated, front face 76 of hollow piston 15 is in contact with the drilling mud circulating inside axial cavity 2 of tubular body 1. These muds are able to accumulate in annular chamber 60, through radial holes 19 in communication with axial cavity 2. Rear faces 77 and 78 of hollow piston 15 are in abutment with the projection 16 of transmission element 10 and a return spring seat 73, respectively. A return spring 18 and the transmission element 10 are in fluid communication with the drilling fluid circulating outside tubular body 1 through the opening of the housings 3. Return spring 18 and transmission element 10 are therefore exposed to the pressure of the hydraulic fluid present in the borehole, i.e., the drilling fluid circulating outside tubular body 1. Return spring 18 also abuts tubular body 1 at an end of return spring 18 opposite that abutting return spring seat 73.

Hollow piston 15 may slide between two positions. A first position illustrated in FIG. 1 is realized when the internal hydraulic pressure does not exceed the external pressure plus the force of return spring 18. A second position illustrated in FIG. 2 is realized when the internal hydraulic pressure exceeds the external pressure plus the force of return spring 18. When the internal pressure exceeds the external pressure plus the force of return spring 18, return spring 18 is compressed by movement of hollow piston 15 upwards. This movement causes an upward movement of transmission element 10, and a deployment of cutting arms 5 and 6 to the extended position.

In any position of hollow piston 15, hollow piston 15 closes off fluid communication between housings 3 and axial cavity 2. However, hollow piston 15 allows drilling muds to circulate through axial cavity 2 of the tool.

As can be seen in FIGS. 1 and 2, cutting arms 5 and 6 and transmission element 10 each have a width corresponding to the distance between the two lateral walls 21 and 22. When moving between the retracted and extended positions, cutting arms 5 and 6 slide along lateral walls 21 and 22, and transmission element 10 moves along lateral walls 21 and 22 and over bottom 20 of housing 3. During this movement, the space 14 is not open to the outside.

As illustrated in FIG. 2, in the extended position of cutting arms 5 and 6, cutting arm 5 and front wall 23 of the housing bear on each other through mutually cooperating surfaces at 25. Likewise, cutting arm 5 and cutting arm 6 bear on each other through mutually cooperating surfaces at 26. Cutting arm 6 and the end of transmission element 10 on which it is articulated bear on each other through mutually cooperating surfaces at 27. This arrangement allows, in the extended position of the cutting arms 5 and 6, transmission of the external forces exerted on cutting arms 5 and 6 from cutting arms 5 and 6 to tubular body 1.

In the extended position, cutting arms 5 and 6 are designed to be largely supported by lateral walls 21 and 22 against the forces exerted by the resistance of the formation to be eroded during the rotation of the tool. Lateral walls 21 and 22 of housing 3 also frame transmission elements 10. Only pivot shaft 8 of cutting arms 5 and 6 is situated outside housing 3, while pivot shafts 7 and 9 are disposed within housing 3. The resistance forces exerted by the formation to be eroded during the forward progression of the tool and the forces exerted by the tool on the formation by cutting arms 5 and 6 are principally absorbed by cutting arms 5 and 6 and transmission element 10. This relieves pivot axes 7, 8 and 9 of the majority of these stresses.

The reaming tool 80 is but one example of a downhole tool on which and or in which stagnation and accumulation of particles may occur and the description herein of the use of a carbon nanoforest with a reamer is not meant to be limiting to the particular reamer disclosed in this example. Thus, the principles described herein may also be used with other downhole tools that may be susceptible to particle stagnation or accumulation.

FIG. 3 is an enlarged cross-sectional side view of a portion of the reaming tool 80 of FIGS. 1 and 2. As illustrated in FIG. 3, a gap 84 may be present between the hollow piston 15 and the tubular body 1. As used herein, the term “gap” may include a joint, passage, channel, cavity, or other space associated with a downhole tool. The distance between the hollow piston 15 and the tubular body 1, and thus the height, H, of the gap 84, may be a constant distance or may instead vary along the length of the gap 84. A first end of the gap 84 defined by front wall 24 fluidly communicates with the elongate slot 17 and thus fluids that may be external to tubular body 1.

A nanoforest filter 121 is strategically positioned a distance, D, from the first end of the gap 84. In some embodiments, the ratio of the distance D to the height H (D:H) is between about 0.1 and about 1. In other embodiments, the D:H may be approximately zero, or even greater than 1. The nanoforest filter 121 may be coupled to a surface associated with either or both of the hollow piston 15 and the tubular body 1. When the nanoforest filter 121 is coupled to the tubular body 1, the value of D remains constant as the reaming tool 80 operates. If the nanoforest filter 121 is coupled to the hollow piston 15, the value of D changes as the piston axially moves within the tubular body.

A circulation zone 86 is present near the first end of the gap 84 and may also include the region within the gap 84 between the front wall 24 and the nanoforest filter 121. The circulation zone 86 is in fluid communication with the elongate slot 17 and thus also fluidly communicates with regions external to the tubular body 1. The nanoforest filter 121 acts as a filter to the gap 84 to prevent accumulation of particles in an accumulation zone 122 associated with gap 84. Without the presence of the nanoforest filter 121, particles may collect in the accumulation zone 122 as the reaming tool 80 is used or deployed downhole. This collection of particles could potentially form a hard and concentrated “pack” of particles that hinders the operation of reaming tool 80 by obstructing movement of adjacent parts, such as for example, the hollow piston 15 and relative to the tubular body 1. A reduction in the ability of hollow piston 15 to move may result in a decreased ability of the cutting arms 5 and 6 to be placed in the extended or retracted positions.

In the absence of the nanoforest filter 121, a pack of particles could otherwise form in the accumulation zone 122 or elsewhere in the gap 84. Many different types of material may form a pack, but typically the pack is formed of assorted cuttings and other particles that have joined together to form a cement-like object or obstruction. In some cases, the particles may include binder materials. Particles related to slacked lime type cement and hydraulic type cement may be in the fluids resulting from drilling. In the case of hydraulic type cement, heating near drilling elements may cause settled particles to have a reduced liquid content and, therefore, result in a solid accumulation.

With the inclusion of nanoforest filter 121, free access of particles to the accumulation zone 122 is substantially reduced. Particles may temporarily accumulate in or near the circulation zone 86, but circulation of fluid through the circulation zone 86 prevents or reduces large scale accumulation of particles or the accumulation of packs. Similarly, the circulation of fluid in the circulation zone 86 and near the nanoforest filter 121 assists in dislodging and removing particles that become lodged in the nanoforest filter 121 near the circulation zone 86.

In some embodiments, the circulation zone 86 is in fluid communication with the accumulation zone 122 but the presence of the nanoforest filter 121 between the accumulation zone 122 and the circulation zone 86 restricts particles that may be present in fluid circulating in the circulation zone 86 from reaching the accumulation zone 122.

The nanoforest filter 121 is configured to catch particles or cuttings that result from drilling operations or are otherwise present in the downhole environment. In some embodiments, nanoforest filter 121 may be characterized by a lower density of nanotubes or other nanostructures than an ordinary nanoforest. A lower density nanoforest filter may allow for some flow of fluids into or through the nanoforest filter 121 but the prevention of the movement of particles past the nanoforest filter 121. This presence of the nanoforest filter 121 prevents the formation of packs in unwanted areas. Additionally, the length of the nanotubes or rods grown in this configuration typically may be longer in length, up to on the order of millimeters long, and grown such that the density of the nanotubes is not great, since the carbon nanoforest is designed to act as a filter rather than a more solid barrier to the penetration of particles.

In some embodiments, nanotubes of a variety of sizes may be grown, with typical heights from 10 to 100 micrometers and diameters from 10 to 100 nanometers. In other embodiments, when the carbon nanoforest is to span a gap that is a millimeter or more, the height of the carbon nanoforest may be greater, on the order of millimeters. Typical particle size in resulting drilling operations is on the order 1 to 100 micrometers. Therefore, the density of nanotubes in the carbon nanoforest may be designed to correspond to these or other expected particle sizes. In areas where increased flow of fluids though the carbon nanoforest is necessary, the density of the carbon nanoforest may be reduced, such that the distance between nanotubes approaches 1 micrometer (or more in some embodiments). Where increased flow is not necessary, a more tightly packed carbon nanoforest may be utilized.

FIG. 4 is an elevation view of a drilling rig 208 having a downhole tool 209 with carbon nanoforests according to an illustrative embodiment. The drilling rig 208 employs sections of pipe 210 to form a drill string that is capable of transferring rotational force to a drill bit 200. A pump 212 may be provided to circulate drilling fluid (as represented by arrows A) to the bottom of the wellbore through the sections of pipe 210 and back to the surface through an annulus between the pipe 210 and the wellbore. As the drill bit rotates, the applied weight-on bit (“WOB”) forces cutters of the drill bit 200 into a substrate being drilled. The cutters of the drill bit 200 apply a compressive force to the substrate which exceeds the yield stress of the substrate, and induces fracturing in the substrate. The resulting fragments (also referred to as “cuttings”) are flushed away from a cutting face of the drill bit 200 by the drilling fluid or “mud” flowing past the drill bit 200.

Rotary joints, static joints, and the like in a variety of wellbore tools are many times not sealed to the annular pressure and flow of drilling muds. Due to tolerances necessary in manufacturing and assembly of these tools, relatively large gaps can result. In many of these joints, enlarged spaces or cavities also are present. These spaces may become accumulation zones and may collect drilling particles that eventually interfere with the operations of the tool. Therefore, nanoforests may be deployed at any joint, space, or cavity in which or through which it is desired to prevent or reduce the accumulation of particles. In some embodiments, the joint or cavity at which the nanoforest is deployed may be between two components or parts that move relative to one another. An example of a wellbore tool that may be used with the drilling rig 208 of FIG. 4 is the reaming tool 80 described with reference to FIGS. 1-3.

FIGS. 5A and 5B are cross-sectional side and end views, respectively, of a downhole tool 409 having an exemplary gap 400 between a first element 404 and a second element 408. The downhole tool 409 may be any particular downhole tool and is not limited to the examples of downhole tools described previously, such as the reaming tool 80 of FIGS. 1-3 and the downhole tool 209 of FIG. 4. While described as a gap, gap 400 could instead be a channel, passage, joint, cavity, space, or other zone or area associated with a downhole tool within which it is desired to reduce or prevent the accumulation of particles.

Referring still to FIGS. 5A and 5B, a carbon nanoforest 420 may be strategically arranged between the first element 404 and the second element 408. In some embodiments, carbon nanoforest 420 may act as a filter to reduce or prevent the access of cuttings 436 or other particles to an accumulation zone 418 (FIG. 5A), thereby preventing the formation of what would be a pack 422 had the carbon nanoforest 420 not been present. FIG. 5A further illustrates how drilling fluid including cuttings 436 flows in gap 400 and contacts carbon nanoforest 420. Fluid and cuttings 436 circulating or otherwise flowing in or through the gap 400 may encounter the carbon nanoforest 410, and some cuttings 436 may return to the wellbore (arrow A), while some cuttings 436 may partially penetrate (arrow B) carbon nanoforest 420. Carbon nanoforest 420 may be configured to obstruct the majority of cuttings 436, allowing the particles to recirculate out of gap 400 with the fluid (arrow A) and substantially filter the other cuttings 436 that are carried with the fluid that traverses carbon nanoforest 420 (arrow B). FIG. 5B illustrates an end view of the gap 400 of FIG. 5A taken at 5B-5B and illustrates a plurality of cuttings 436 trapped within carbon nanoforest 420.

FIGS. 6A and 6B are side views of yet another embodiment of a reaming tool 500 having a nanoforest filter 505 arranged in a gap, joint, channel, cavity, space, area, or other zone within which it is desired to reduce or prevent the accumulation of particles. The reaming tool 500 includes a tubular body 510 and cutter blocks 520, which in FIG. 6A are shown in a retracted position. Like cutting arms 5 and 6 of FIGS. 1-3, cutter blocks 520 may be moved into an extended position (FIG. 6B) to enlarge the size of a wellbore in which the reaming tool 500 is deployed and rotated. The reaming tool 500 may include multiple actuation components internal to the tubular body 510 and which are not illustrated in FIGS. 6A and 6B. These components are capable of cooperating to extend and retract the cutter blocks 520. The joints or gaps between these actuation components are a few examples of the locations in which it may be desirable to include the nanoforest filter 505.

In addition to reducing or preventing particle accumulation in certain areas or zones of downhole tools, the presence of nanoforests in downhole tools may also assist in tool lubrication. As the carbon nanoforest wears, the byproduct will include nanotube segments, graphene, or few layer graphene, all of which are effective lubricants. Moreover, the carbon nanoforest may prove useful in providing protection to the mating surface to which the carbon nanoforest is coupled, which may further extend the lifetime of the wellbore tool.

FIG. 7 is a schematic view of a carbon nanoforest being grown on a mating surface of a joint. Instead of bonding or otherwise attaching carbon nanoforests to mating surfaces as described herein, the carbon nanoforests may be grown on a mating surface 724 of an element 726 of a joint by providing a plurality of densely packed nanoparticle catalysts 734 on the mating surface 724 and exposing the nanoparticle catalysts 734 to carbon nanostructure growth conditions for a period of time to achieve a carbon nanoforest 728 of a desired height.

FIG. 8 illustrates sequential schematics demonstrating growth of a carbon nanoforest on a substrate and then either adhering the substrate to a mating surface (A1) or adhering the carbon nanoforests to the mating surface (B1) and subsequently removing the substrate (B2). More particularly, a plurality of densely packed nanoparticle catalysts 834 may be provided on a substrate 830, and the nanoparticle catalysts 834 may be exposed to carbon nanostructure growth conditions for a time period so as to achieve a carbon nanoforest 828 with a desired height. The substrate 830 may then be adhered or otherwise coupled to a portion of a mating surface 824 of an element 826 of a joint with an adhesive 832 (e.g., illustrated in A2 of FIG. 8).

Alternatively, the carbon nanoforest 828 itself may be adhered or otherwise coupled to a portion of a the mating surface 824 of the element 826 of the joint with the adhesive 832 (e.g., illustrated in B1 of FIG. 8). The carbon nanoforest may be separated from the substrate 830 (e.g., illustrated in B2 FIG. 8).

Preventing the formation of a pack in key areas of downhole tools is an important factor in being able to continuously perform drilling operations. By deploying carbon nanoforests as either filters or structures to prevent pack formation in a certain area, carbon nanoforests may improve the operation of downhole tools. In addition to the embodiments described above, many examples of specific combinations are within the scope of the disclosure, some of which are detailed below.

EXAMPLE 1

A reaming tool comprising:

a tubular body having an axial cavity and a plurality of housings, each of the housings having an opening through a periphery of the tubular body;

a cutter element positioned in each of the housings, the cutter element movable between a retracted position and an extended position;

a drive mechanism positioned within the tubular body and movable relative to the tubular body to extend or retract each cutter element;

a gap defined between the drive mechanism and the tubular body;

a carbon nanotube forest coupled to one of the drive mechanism and the tubular body to reduce or prevent accumulation of particles in the gap.

EXAMPLE 2

The reaming tool of example 1, wherein carbon nanotube forest is positioned within the gap.

EXAMPLE 3

The reaming tool of example 1, wherein the drive mechanism is a hollow piston that is capable of axially moving within the tubular body to extend or retract each cutter element.

EXAMPLE 4

The reaming tool of example 1 further comprising:

a circulation zone within each housing that receives fluid and particles from an exterior region of the reaming tool; and

an accumulation zone within the gap;

wherein the carbon nanotube forest is positioned within the gap between the circulation zone and the accumulation zone.

EXAMPLE 5

The reaming tool of example 4, wherein the carbon nanotube forest is in fluid communication with both the circulation zone and the accumulation zone.

EXAMPLE 6

The reaming tool of example 1, wherein:

the carbon nanotube forest is positioned within the gap and a distance, D, from an end of the gap;

the gap has a height, H; and

the ratio of D:H is between about 0.1 and about 1.

EXAMPLE 7

The reaming tool of example 6 further comprising:

a circulation zone within each housing that receives fluid and particles from an exterior region of the reaming tool; and

an accumulation zone within the gap;

wherein the carbon nanotube forest is positioned within the gap between the circulation zone and the accumulation zone;

wherein the circulation zone extends into the gap the distance D.

EXAMPLE 8

A downhole tool, comprising:

a circulation zone in fluid communication with an exterior region of the downhole tool;

an accumulation zone;

a carbon nanotube forest coupled to a portion of the downhole tool and positioned in fluid communication with both the circulation zone and the accumulation zone, the carbon nanotube forest reducing or preventing particles in the circulation zone from accumulating in the accumulation zone.

EXAMPLE 9

The downhole tool of example 8, wherein the carbon nanotube forest includes nanotubes spaced apart not more than 1 micrometer.

EXAMPLE 10

The downhole tool of example 8, wherein the carbon nanotube forest includes nanotubes having heights of between about 10 micrometers and 100 micrometers.

EXAMPLE 11

The downhole tool of example 8, wherein the carbon nanotube forest includes nanotubes having diameters of between about 10 nanometers and 100 nanometers.

EXAMPLE 12

The downhole tool of example 8 further comprising:

a gap defined between a first element and a second element;

wherein the accumulation zone is a region within the gap; and

wherein the carbon nanotube forest is positioned within the gap and is coupled to at least one of the first and second element.

EXAMPLE 13

The downhole tool of example 12, wherein:

at least a portion of the circulation zone is in the gap; and

the carbon nanotube forest is arranged between the circulation zone and the accumulation zone.

EXAMPLE 14

The downhole tool of example 8, wherein the first element is capable of movement relative to the second element during operation of the downhole tool.

EXAMPLE 15

A method for reducing or preventing the accumulation of particles in a downhole tool, the method comprising:

identifying an accumulation zone inside the downhole tool where particle accumulation is possible; and

arranging a carbon nanoforest in fluid communication with the accumulation zone to filter a particle that would otherwise accumulate at the accumulation zone.

EXAMPLE 16

The method of example 15, further comprising:

identifying a circulation zone associated with the downhole tool that is capable of receiving fluid and particles from an exterior region of the downhole tool; and

positioning the carbon nanoforest between the circulation zone and the accumulation zone.

EXAMPLE 17

The method of example 15, wherein arranging the carbon nanoforest further comprises coupling the carbon nanoforest to at least one element of the downhole tool.

EXAMPLE 18

The method of example 17, wherein the downhole tool is a remaining tool and the at least one element is a one of a tubular body and a hollow piston.

EXAMPLE 19

The method of example 15, wherein arranging the carbon nanoforest further comprises positioning the carbon nanoforest within a gap defined between a first element and a second element of the downhole tool.

EXAMPLE 20

The method of example 15, wherein identifying the accumulation zone is performed using fluid flow analysis techniques to identify areas where stagnant flow is possible.

It should be apparent from the foregoing that the various features embodied in the disclosed example embodiments are not limited to only those example embodiments. Various changes and modifications are possible without departing from the spirit thereof. 

What is claimed:
 1. A reaming tool comprising: a tubular body having an axial cavity and a plurality of openings through a periphery of the tubular body; a plurality of cutter elements positioned in the tubular body, each cutter element movable through a respective one of the openings between a retracted position and an extended position; a drive mechanism within the tubular body and movable relative to the tubular body to extend or retract each cutter element; a gap defined between the drive mechanism and the tubular body; and a carbon nanotube forest coupled to one of the drive mechanism and the tubular body to reduce or prevent accumulation of particles in the gap.
 2. The reaming tool of claim 1, wherein the tubular body comprises a plurality of housings, each containing a respective one of the cutter elements and defining a respective one of the openings.
 3. The reaming tool of claim 1, wherein carbon nanotube forest is positioned within the gap.
 4. The reaming tool of claim 1, wherein the drive mechanism comprises: a hollow piston that is axially movable within the tubular body to extend or retract each cutter element.
 5. The reaming tool of claim 2 further comprising: a circulation zone within each housing that receives fluid and particles from an exterior region of the reaming tool; and an accumulation zone within the gap; wherein the carbon nanotube forest is positioned within the gap between the circulation zone and the accumulation zone.
 6. The reaming tool of claim 5, wherein the carbon nanotube forest is in fluid communication with both the circulation zone and the accumulation zone.
 7. The reaming tool of claim 1, wherein: the carbon nanotube forest is positioned within the gap and a distance, D, from an end of the gap; the gap has a height, H; and the ratio of D:H is between about 0.1 and about
 1. 8. The reaming tool of claim 7, wherein the tubular body comprises a plurality of housings, each containing a respective one of the cutter elements and defining a respective one of the openings, the reaming tool further comprising: a circulation zone within each housing that receives fluid and particles from an exterior region of the reaming tool; and an accumulation zone within the gap; wherein the carbon nanotube forest is positioned within the gap between the circulation zone and the accumulation zone; wherein the circulation zone extends into the gap the distance D.
 9. A downhole tool, comprising: a circulation zone in fluid communication with an exterior region of the downhole tool; an accumulation zone; a carbon nanotube forest coupled to a portion of the downhole tool and positioned in fluid communication with both the circulation zone and the accumulation zone, the carbon nanotube forest reducing or preventing particles in the circulation zone from accumulating in the accumulation zone.
 10. The downhole tool of claim 9, wherein the carbon nanotube forest includes nanotubes spaced apart not more than 1 micrometer.
 11. The downhole tool of claim 9, wherein the carbon nanotube forest includes nanotubes having heights of between about 10 micrometers and 100 micrometers.
 12. The downhole tool of claim 9, wherein the carbon nanotube forest includes nanotubes having diameters of between about 10 nanometers and 100 nanometers.
 13. The downhole tool of claim 9 further comprising: a gap defined between a first element and a second element; wherein the accumulation zone is a region within the gap; and wherein the carbon nanotube forest is positioned within the gap and is coupled to at least one of the first and second element.
 14. The downhole tool of claim 13, wherein: at least a portion of the circulation zone is in the gap; and the carbon nanotube forest is arranged between the circulation zone and the accumulation zone.
 15. The downhole tool of claim 9, wherein the first element is capable of movement relative to the second element during operation of the downhole tool.
 16. A method for reducing or preventing the accumulation of particles in a downhole tool, the method comprising: identifying an accumulation zone inside the downhole tool where particle accumulation is possible; and arranging a carbon nanoforest in fluid communication with the accumulation zone to filter a particle that would otherwise accumulate at the accumulation zone.
 17. The method of claim 16 further comprising: identifying a circulation zone associated with the downhole tool that is capable of receiving fluid and particles from an exterior region of the downhole tool; and positioning the carbon nanoforest between the circulation zone and the accumulation zone.
 18. The method of claim 16, wherein arranging the carbon nanoforest further comprises coupling the carbon nanoforest to at least one element of the downhole tool.
 19. The method of claim 18, wherein the downhole tool is a remaining tool and the at least one element is a one of a tubular body and a hollow piston.
 20. The method of claim 16, wherein arranging the carbon nanoforest further comprises positioning the carbon nanoforest within a gap defined between a first element and a second element of the downhole tool.
 21. The method of claim 16, wherein identifying the accumulation zone is performed using fluid flow analysis techniques to identify areas where stagnant flow is possible. 